Roughly chop herbs and add to garlic, crush to combine.
Gently ease the skin away from the meat over the chicken breasts from the neck end (ie not from the cavity). Take some of the garlic-herb mixture and push it in under the skin, over the breast, on each side, and ease it over as much of the breast as possible by rubbing from the outside once you have put the mixture in as best you can. Rub the rest of the paste over the outside.
Cut the half lemon in two and push into the cavity of the bird, then place on a roasting tray. Slice the butter into 3 or 4 thin slices and put a slice under the skin on each breast.
Sprinkle the skin with salt and pepper then drizzle over a little olive oil and rub in. Dot a couple more pieces of butter on the outside.
Roast for 1hr, 15 mins until the skin is crisp and the juices run clear.